weather.com for your zip code
I find the weekend outlook, 10 day forecast and especially the hour by hour links
to be especially helpful for planning astronomy outings, even if I am only going
to the back porch. Just put in your zip code, click the findlocation button,
select a category (I picked Home Planner), and click Save Changes (I don't know
if the demographic info is required, it's just gender and year of birth, so I just
gave it). That will take you to your local weather page which you can bookmark
for future visits.

Water Vapor Maps
Sometimes when the forecast is for clear skies and you don't see any clouds you
may still not have the best visibility. This link to the NOAA website has
maps for the east US, west US, Hawaii, Alaska and Puerto Rico. The visible
map, of course, is useless at night, but the water vapor map is useful 24 hours
a day. It is always about an hour behind, but if you click on the movie link
you get a 3.5 hour loop so you can have an idea of what is heading your way.
There are actually two links for animated loops. If you use the one I have
pointed to with the red arrow there is also a zoom button; click that and then click
your location in the map and it will zoom in to that area.